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Like you said, you can't license a right.


It is not as simple as that.
For example, all individuals within an certain age bracket are considered to be members of the unorganised militia. It is possible to force all these people to participate in the militia. Making people take a 1 hour course every five years as their militia service can be done. People who do not participate are therefore breaking the law.
YOu break the law, through due process the govt can take away your RKBA.

What the feds cannot do is make a law which would prohibit the majority of the people from keeping and bearing arms. In 1792 with the passing of the militia act, we know that forcing people to bear arms is not unconstitutional, so, the registering of individuals into the militia is not unconstitutional as it is a militia, you have to know who your soldiers are.